The discovery in early nineties of the coupling of lightning energy to the upper atmosphere and the associated phenomena observed in a wide spectral range has been a big surprise.  These phenomena are grouped under the name "high altitude lightning" and include red sprites, elves, blue jets, gamma-ray flashes, radio bursts and others. The red sprites and elves, generated due to conventional breakdown caused by static field or electromagnetic pulses (EMP) from lightning, are the best understood among these phenomena.

  Three phenomena were prime focus of the research conducted by the SPP: the high altitude optical flashes, termed red sprites, the narrow cones of blue light that propagate upward from the top of the top of a thundercloud called blue jets, and gamma-ray flashes observed by a satellite based detector [Gurevich et al.¹, 1996; Milikh and Valdivia², 1999;  Kaw et al.³, 2001; Milikh et al⁴, 2005].

  In the case of red sprites emphasis was on developing a model of its streamer structure.  A two step approach was adopted to fulfill this objective. First, the EMP generated during the discharge process in intracloud lightning creates localized patches of conductivity and ionization having a wide range of scales in the lower ionosphere. The patchy structure is a consequence of the fact that intracloud lightning radiates as a fractal antenna with interference patterns corresponding to fractal arrays rather than line radiators [Valdivia⁵ et al.⁶, 1997, 1998]. Second, the interaction of the patchy inhomogeneous conductivity structure with the laminar thunderstorm field   left in the ionosphere over a dielectric relaxation time was considered. The conducting patches act as catalysts that drive streamers when interacting with the laminar field of the thundercloud [Raizer et al.⁷, 1998]. The output of the model was the spectrum of the sprite [Milikh⁸ et al.⁹, 1996, 1998] (bottom figure) along with the streamer charge and propagation speed.

        Recently a new model of blue jets was proposed [Raizer et al.^10,11, 2006, 2007].  A blue jet consists of the bi-leader, whose top part is seen on photos as a trunk of a tree, and is capped at the top side of the leader by its streamer zone (left figure). Two leaders one of them moving upward while the other moves downward feed each other with the charge and current without any involvement of the cloud charge. Similarly, bi-leaders are formed in the ordinary lightning. It was shown that due to transfer of the high potential of the edge of the thundercloud by the leader, long streamers of blue jets can be sustained by moderate cloud charge. The model estimates the streamer length along with the height at which the streamers can reach the ionosphere.  The propagation of a streamer in the exponential

References

1.     Runaway Electrons in the Atmosphere in the Presence of Magnetic Field, A.V. Gurevich, J. A. Valdivia, G.M. Milikh and K. Papadopoulos, Radio Sci., 31, 1541-1554, 1996.

2.     Model of Gamma Ray Flashes due to Fractal Lightning, G. M. Milikh and J. A. Valdivia, Geophys. Res. Lett., 26, 525-528, 1999.

3.     Gamma ray flashes by plasma effects in middle atmosphere, P. K. Kaw, G. M. Milikh, A. S. Sharma, P. N. Guzdar and K. Papadopoulos, Phys. Plasmas, 8(11), 4954-4959, 2001.

4.     Gamma ray flashes due to plasma processes in the atmosphere: Role of whistler waves, G. M. Milikh, P.N. Guzdar, and A. S. Sharma, J. Geophys. Res., 110, A02308, doi:10.1029/2004JA010681, 2005.

5.     Red Sprites: Lightning as a Fractal Antenna, J. A. Valdivia, G.M. Milikh and K. Papadopoulos, Geophys. Res. Lett., 24, 3169-3172, 1997.

6.     Model of Red Sprites Due to Intracloud Fractal Lightning, J. A. Valdivia, G.M. Milikh and K. Papadopoulos, Radio Sci., 33, 1655-1668, 1998.

7.     Long Streamers in the Upper Atmosphere Above Thundercloud, Yu. P. Raizer, G. M. Milikh, M. N. Shneider and S. V. Novakovski, J. Phys. D: Applied Phys., 31, 3255-3264, 1998.

8.     Spectrum of Red sprites, G. M. Milikh, J. A. Valdivia, and K. Papadopoulos, J. Atmos. & Solar-Terr Phys., 60, 907-915, 1998.

9.     Model of Red Sprites Due to Intracloud Fractal Lightning, J. A. Valdivia, G.M. Milikh and K. Papadopoulos, Radio Sci., 33, 1655-1668, 1998.

10.  Leader streamer nature of blue jets, Y. P. Raizer, G. M. Milikh, and M. N. Shneider, J. Atmos. & Solar-Terr Phys., 69, 925-938, doi:10.1016/j.jastp.2007.02.007, 2007.

11.  On the mechanism of blue jet formation and propagation, Y. P. Raizer, G. M. Milikh, and M. N. Shneider, Geophys. Res. Lett., 33, L23801, doi:10.1029/2006GL027697, 2006.